import numpy as np
import torch
from torch import nn
from torch.nn import init


class PSA(nn.Module):

    def __init__(self, channel=512, reduction=4, S=4):
        super().__init__()
        self.S = S

        self.convs = []
        for i in range(S):
            self.convs.append(nn.Conv2d(channel // S, channel // S, kernel_size=2 * (i + 1) + 1, padding=i + 1))

        self.se_blocks = []
        for i in range(S):
            self.se_blocks.append(nn.Sequential(
                nn.AdaptiveAvgPool2d(1),
                nn.Conv2d(channel // S, channel // (S * reduction), kernel_size=1, bias=False),
                nn.ReLU(inplace=True),
                nn.Conv2d(channel // (S * reduction), channel // S, kernel_size=1, bias=False),
                nn.Sigmoid()
            ))

        self.softmax = nn.Softmax(dim=1)

    def init_weights(self):
        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                init.kaiming_normal_(m.weight, mode='fan_out')
                if m.bias is not None:
                    init.constant_(m.bias, 0)
            elif isinstance(m, nn.BatchNorm2d):
                init.constant_(m.weight, 1)
                init.constant_(m.bias, 0)
            elif isinstance(m, nn.Linear):
                init.normal_(m.weight, std=0.001)
                if m.bias is not None:
                    init.constant_(m.bias, 0)

    def forward(self, x):
        b, c, h, w = x.size()

        # Step1:SPC module
        SPC_out = x.view(b, self.S, c // self.S, h, w)  # bs,s,ci,h,w
        for idx, conv in enumerate(self.convs):
            SPC_out[:, idx, :, :, :] = conv(SPC_out[:, idx, :, :, :])

        # Step2:SE weight
        se_out = []
        for idx, se in enumerate(self.se_blocks):
            se_out.append(se(SPC_out[:, idx, :, :, :]))
        SE_out = torch.stack(se_out, dim=1)
        SE_out = SE_out.expand_as(SPC_out)

        # Step3:Softmax
        softmax_out = self.softmax(SE_out)

        # Step4:SPA
        PSA_out = SPC_out * softmax_out
        PSA_out = PSA_out.view(b, -1, h, w)

        return PSA_out


if __name__ == '__main__':
    input = torch.randn(50, 512, 7, 7)
    psa = PSA(channel=512, reduction=8)
    output = psa(input)
    a = output.view(-1).sum()
    a.backward()
    print(output.shape)

